Significant Accounting Policies - Investment in Marketable Securities (Details)	12 Months Ended
	Dec. 31, 2021 USD ($) security	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Investment in Marketable Securities
Marketable securities available-for-sale	$ 24,146,000	$ 28,570,000
Investments in marketable securities	34,752,000	28,570,000
Marketable securities, unrealized gain	600,000
Proceeds from sale of marketable securities	4,500,000	0	$ 0
Proceeds from sale of equity marketable securities	$ 0
Number of marketable securities sold | security	1
Fair Value
Investment in Marketable Securities
Marketable securities available-for-sale	$ 24,146,000	28,570,000
Investments in marketable securities	34,752,000	28,570,000
Commercial mortgage-backed securities
Investment in Marketable Securities
Marketable securities available-for-sale	24,146,000	28,570,000
Cost basis of commercial mortgage backed securities	$ 23,000,000	27,500,000
Number of securities in continuous unrealized loss position | security	1
Unrealized loss	$ 600,000	700,000
Fair value of security in a continuous unrealized loss position for less than 12 months	7,200,000	7,000,000
Equity marketable securities
Investment in Marketable Securities
Investments in marketable securities	$ 10,606,000	$ 0